Magnetic Resonance Sequences and Rapid Acquisition for MR-Guided Interventions

Abstract

Interventional MR uses rapid imaging to guide diagnostic and therapeutic procedures. One of the attractions of MR-guidance is the abundance of inherent contrast mechanisms available. Dynamic procedural guidance with real-time imaging has pushed the limits of MR technology, demanding rapid acquisition and reconstruction paired with interactive control and device visualization. This article reviews the technical aspects of real-time MR sequences that enable MR-guided interventions.

Keywords: MR image reconstruction; Non-Cartesian imaging; Parallel imaging; Real-time MR imaging.

Figure 1

Diagram of real-time acquisition running continuously with multiple slices updating in rapid succession. Image contrast is changed using an optional magnetization preparation module and interactive parameter control. bSSFP, balanced steady-state free precession.

Figure 2

Virtual dye angiography uses volume selective-saturation pulses to saturated blood signal locally. The difference images between saturation off/on (black and white images) are used to produce a color-flow map. Ao, aorta; LA, left atrium; LV, left ventricle. (From George AK, Faranesh AZ, Ratnayaka K, et al. Virtual dye angiography: flow visualization for MRI-guided interventions. Magn Reson Med 2012;67(4):1013–21; with permission.)

Figure 3

Illustration of SENSE reconstruction using undersampled aliased images and coil sensitivity maps. (Data from Collins DL, Zijdenbos AP, Kollokian V, et al. Design and construction of a realistic digital brain phantom. IEEE Trans Med Imaging 1998;17(3):463–8; and BrainWeb: Simulated Brain Database. Available at: http://brainweb.bic.mni.mcgill.ca/brainweb/.)

Figure 4

Spin warp Cartesian imaging (a) compared to more efficient k-space trajectories: echo planar imaging (b), spiral (c), and radial k-space trajectories (d).

Figure 5

Right heart catheterization using real-time MR imaging to navigate a gadolinium-filled balloon (arrows) between cardiac chambers. Standard real-time bSSFP (A, C, E) and real-time bSSFP with saturation prepulses (B, D, F) are depicted. Saturation prepulses are used to isolate the gadolinium-filled balloon signal. (From Ratnayaka K, Faranesh AZ, Hansen MS, et al. Real-time MRI-guided right heart catheterization in adults using passive catheters. Eur Heart J 2013;34(5):380–9; with permission.)

Figure 6

(A–D) Active microcoil (arrow) tracking of brachytherapy stylet. The trajectory (yellow points) represents consecutive tracking positions overlaid on previously acquired images. (From Wang W, Dumoulin CL, Viswanathan AN, et al. Real-time active MR-tracking of metallic stylets in MR-guided radiation therapy. Magn Reson Med 2015;73(5):1810; with permission.)

Figure 7

Overview of the imaging infrastructure that could be used in the interventional MR imaging environment. The device data can be isolated during reconstruction to permit the color overlay of the device signal in the interactive environment. Dashed lines represent optional components. GPU, graphics processing unit.